Adhesion of active electrode materials to metal electrode substrates

ABSTRACT

A battery electrode for a lithium ion battery that includes an electrically conductive substrate having an electrode layer applied thereto. The electrode layer includes an organic material having high alkalinity, or an organic material which can be dissolved in organic solvents, or an organic material having an imide group(s) and aminoacetal group(s), or an organic material that chelates with or bonds with a metal substrate or that chelates with or bonds with an active material in the electrode layer. The organic material may be guanidine carbonate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application no.13/805,331 filed Feb. 1, 2013, which is a 371 of Internationalapplication no. PCT/AU2011/000812 filed Jun. 30, 2011, which claimspriority to Australian application no. 2010902901 filed Jun. 30, 2010,the entire content of each which are incorporated herein by referencethereto.

FIELD OF INVENTION

The present invention relates to method for achieving improved adhesionof active cathode and anode materials to metal substrates, particularlythose used in lithium-ion secondary batteries.

BACKGROUND

High performance lithium-ion secondary batteries that exhibit highenergy density, fast charge/discharge cycles and long cycle life havebecome increasingly important for the rapid development of the hybridand electric vehicle industry. In addition, large format lithium-ionbatteries look set to also play an important role in energy storage forrenewable and off-peak electricity generation.

Lithium ion secondary batteries typically comprise two electrodes (acathode and an anode) having a porous separator and liquid electrolytematerial positioned between the two electrodes. At least one of theelectrodes, typically the cathode, comprises a metal substrate (whichacts as a current collector) and an electrode material applied bycoating to the metal substrate. The cathode electrode material typicallycomprises a mixture of a lithium-containing compound that provides alithium ion source in the battery, a binder, a solvent and conductiveparticulate material. The anode material typically comprises a carbon orgraphitic type compound that intercalates lithium and a binder, asolvent and conductive particulate material. Aluminium metal is usuallythe substrate for the cathode material. Copper metal is usually thesubstrate for the anode material.

The lithium containing compound in the electrode material may be, forexample, a lithium iron phosphate material (LFP), LiMXO₄ (M: Fe, Mn, Co,Ni, etc. and mixtures of these elements; X: P, Si, Si, V, etc. andmixtures of these elements), Li₂FePO₄F, LiCoO₂,LiCo_(1/3)Ni_(1/3)Mn_(1/3)O₂, LiMn₂O₄, Li₂MnO₃—LiMO₂ (M: Mn, Ni, Co),Li₂SO₄, lithium vanadium oxides, lithium vanadium phosphates, lithiumtitanates, other lithium ion intercalating compounds and/or mixtures andcomposites of any of the aforementioned materials. The lithiumcontaining compound in the electrode material can provide lithium ionsto the electrolyte and receive lithium ions from the electrolyte duringcharging and discharging cycles.

Although the lithium containing compounds allow for higher electricalenergy density during discharge and also allow for a large number ofcharging cycles, they suffer from the drawback that they have relativelylow electrical conductivity. To overcome this difficulty, the electrodematerial is typically provided with conductive particulate material,such as electrically conductive carbon black. The carbon black providesincreased electrical conductivity to the coating. In other electrodecoatings, the lithium containing compound (which is typically in theform of solid particles) may be coated with a graphite layer to provideincreased electrical conductivity.

Manufacturing of electrodes for lithium batteries typically involvescoating the metal substrate with a layer of the electrode material.Manufacturing techniques have developed to rapidly apply a coating ofthe electrode material. These techniques require that the coatinginclude a solvent. A solvent that is commonly used isN-Methyl-2-pyrrolidone (NMP). A binder, which is normally polyvinylidene fluoride (PVDF), is also included.

In order to form the electrode, it is common to provide the electrodematerial in the form of an ink or a liquid composition that can beapplied to the metal substrate using technology similar to printingtechnology. After the coating of the electrode material has been appliedto the substrate, the coating is subjected to a calendaring process topress and heat the coating, which increases the density of the coating.

Two aspects central to achieving high performance in these batteries isgood internal ionic and electrical conductivity. In the case ofelectronic conductivity it is essential to have low impedance at theinterface between the active cathode material and the metal electrodesubstrate. This is achieved by ensuring complete adhesion of the cathodeto the metal substrate.

Adhesion between a coating and a substrate is usually achieved throughone or more of the three following mechanisms:

Surface roughness;

Chemical bonding; and/or

Interface reaction or compound.

With surface roughness, although the compounds that make up thesubstrate and the coating do not necessarily establish a chemical bond,the mechanical interlocking of their rough interface guarantees a goodcontact between the coating and the substrate.

With chemical bonding, the coating must contain ingredients orcomponents that are capable of establishing molecular bonds to thesubstrate. This would ideally be the case, for instance, with mostbinders that are used in the battery cathode ink formulation.

Through an interface reaction, one (or more) new compound(s) istypically formed at the interface and this compound is likely to acquirethe features that facilitate either one or both of the previous twomechanisms of adhesion—surface roughness and chemical bonding.

In the case of lithium-ion secondary batteries significant problems havearisen in achieving good adhesion at this interface between theelectrode material and the metal substrate. Coated electrodes of thistype need to maintain their conductivity while still being flexibleenough to be wound or rolled into final battery shapes. As a result,lithium containing cathode materials are mixed with binders, conductingcarbon particles and solvent to produce an ink that can be cast onto acontinuous roll of metal foil, such as aluminium, that can be later cutinto appropriate lengths and wound with other components to produce thebattery. Furthermore, when good adhesion is achieved between the cathodeand the collector substrate, it is possible to exert higher pressuresduring the process step known as calendering. Such additional pressurewill in turn improve the electrical contact between particles, and also,enhance the packing density, both of which are desirable for enhancedperformance. FIG. 1 shows the gradual reduction in resistance of pressedpellets of plain LFP powder without additional particulate Super P(Super P is the trade name of a carbon black material commonly used inlithium battery manufacture) or binder. As the contact between particlesincreases, so does the conductivity.

As mentioned above, a typical cathode ink composition may contain alithium metal oxide, as the lithium-ion source, polvinylidene fluoride(PVDF) or PVDF copolymer resins as the binder, N-Methyl-2-pyrrolidone(NMP) as the binder solvent and carbon black as a conductive particlesource. Factors such as surface charges, reactions between componentsand final ink pH can result in a mix that has little or no adhesion withmetal electrode substrates. In particular, a good mixing anddistribution of the particulate conducting carbon needs to be obtainedin order to ensure good electrical contact across the entire area andthickness of the cathode coating.

Aluminium, which is usually the substrate for the cathode material, isknown to have a nanometre scale oxide surface layer. Caustic solutionsand very acid solutions dissolve the oxide layer, however, the speed ofre-oxidation after exposure in air at room temperature is known to bevery fast, of the order of microseconds, for the re-establishment of thefirst few nanometers of the aluminium oxide coating. Such oxide layer isexpected to change the surface properties of the substrate and toprovide some degree of electrical insulating contribution.

Cleaning the aluminium substrate with caustic and acidic solution toremove the aluminium oxide layer from the surface of the substrate ispossible. However, it is unlikely that such a step will be a viableprocessing step in electrode manufacture, not only because it introducesadditional steps, but primarily because the aforementioned oxide layerswill re-form quickly, prior to the final coating step with the electrodematerial. In addition, KOH is known to react exothermically and somewhatviolently with aluminium, with generation of hydrogen gas. Thus, itwould be difficult to implement on a large scale.

Finally in order to achieve good adhesion, in addition to introducingone of the aforementioned adhesion mechanisms, a good mixing anddistribution of the particulate conductive material, such as conductingcarbon, needs to be obtained in order to ensure good electrical contactacross the entire area and thickness of the coating.

A number of approaches have been used in an attempt to overcome thisadhesion problem. These approaches include pre-coating the metalelectrode with an interface layer, pretreating the metal surface usingpickling solutions to enhance surface roughness and adding functionalgroups that enhance cross linking of monomers with PVDF copolymersbinders.

A number of efforts, from prior art, to improve the coating of electrodematerials on to metal substrates for use in production of batteries arelisted below.

United States patent application US 2009/0263718 A1 discloses theaddition of two different size ranges of particulate conductive carbon(one with average particle diameter of from 3 to 10 micron and anotherwith average particle diameter of 1 micron or less) is useful to improvethe cohesiveness in the pressing stage and assists to prevent defectssuch as detachment from occurring.

United States patent application US 2009/0155689 A1 discloses the use ofmultimodal particle size distribution in the LiMPO₄ (M: Fe or Mn) activecathode material comprising at least one fraction of micron sizeparticles and at least one fraction of submicron size particles in orderto enhance packing density and optimise porosity. Two differentprocesses are in general used to obtain the materials with differentparticle size distribution. Although the focus is to enhance energydensity and power performance, improvements in cohesiveness similar tothose of patent application US 2009/02673718 A1 may be expected.

United States patent application US 2004/0234858 A1 discloses that whena surface roughness of at least 0.1 micron in the current collector isused, adhesion between the mixed layer and the collector is greatlyimproved.

U.S. Pat. No. 5,399,447 discloses a method to reduce the acidity of anadhesion promoter layer made of carbon and polyacrylic acid by treatingthis layer with LiOH. Otherwise, there is the risk of H+ ions taking theplace of Li+ ions in the cathode material, thereby reducing the capacityof the battery.

International Patent application WO 00/49103 describes a method for theadhesion of vinylidene fluoride resins to metal substrates which ischaracterized in that, when sticking a polyvinylidene fluoride to ametal substrate, there are added to and mixed with vinylidene fluorideresin (a) at least one type of polymer (b) selected from acrylic andmethacrylic polymers or resins containing such polymers and at least oneorganic compound (c) selected from the mercapto, thioether, carboxylicacid and carboxylic anhydride groups.

A method of manufacturing electrodes for electrochemical devices isdisclosed in United States patent application US 2006/0153972 A1. Inthis patent, adhesion is attributable to an electrically conductiveadhesive produced by mixing a particulate rubber and particulateconducting carbon. The role of too little or too much rubber inproportion to carbon is emphasized.

Although the prior art mentioned above teaches ways to improve adhesion,most of these methods introduce additional processing steps in themanufacture of the battery cathodes adding to the complexity and cost.Most battery manufacturers are reluctant to alter their manufacturingpractices significantly. Therefore, it is desirable to provide forenhanced adhesion of the electrode material to the metal substratewithout requiring the introduction of additional steps to the electrodemanufacturing process. Desirably, enhanced adhesion of the electrodematerial should be obtained without requiring any other changes in thecoating manufacturing steps and without any collector/substratepre-treatment in the lithium-ion secondary battery manufacturingindustry, in particular, for powders with various particlescharacteristics and morphologies.

Throughout this specification, the term “comprising” and its grammaticalequivalents shall be taken to have an inclusive meaning unless thecontext of use indicates otherwise.

The applicant does not concede that the prior art discussed in thisspecification forms part of the common general knowledge in Australia orelsewhere.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a composition forforming a battery electrode for a lithium ion battery, the compositioncomprising:

a lithium containing compound that provides a lithium ion source in thebattery;

a binder;

a solvent;

a conductive particulate material; and

an organic material having high alkalinity.

In some aspects, the organic material may be dissolved in an organicsolvent. Accordingly, in a second aspect, the present invention providesa composition for forming a battery electrode for a lithium ion battery,the composition comprising:

a lithium containing compound that provides a lithium ion source in thebattery;

a binder;

a solvent;

a conductive particulate material; and

an organic material having high alkalinity which can be dissolved inorganic solvents

In a third aspect, the present invention provides a composition forforming a battery electrode for a lithium ion battery, the compositioncomprising:

a lithium containing compound that provides a lithium ion source in thebattery;

a binder;

a solvent;

a conductive particulate material; and

an organic material having imide group(s) and aminoacetal group(s).

In a fourth aspect, the present invention provides a composition forforming a battery electrode for a lithium ion battery, the compositioncomprising:

a lithium containing compound that provides a lithium ion source in thebattery;

a binder;

a solvent;

a conductive particulate material; and

an organic material that chelates or bonds with a metal substrate and/orwith an active ingredient in the electrode layer. The active ingredientthat the organic compound may chelate with or bond with may comprise theconductive particulate material . The conductive particulate materialmay be a carbonaceous material. In embodiments where the organicmaterial chelates with the metal substrate or with the activeingredient, the organic material may strongly chelate with the metalsubstrate or with the active ingredient.

In a fifth aspect, the present invention provides a composition forforming a battery electrode for a lithium ion battery, the compositioncomprising:

a graphitic type compound that intercalates lithium,

a binder;

a solvent;

a conductive particulate material; and

an organic material that chelates or bonds with a metal substrate and/orwith the conductive particulate material. The conductive particulatematerial may be a carbonaceous material. In embodiments where theorganic material chelates with the metal substrate or with theconductive particulate material, the organic material may stronglychelate with the metal substrate or with the conductive particulatematerial.

The composition of the first aspect, second aspect, third aspect, fourthaspect and fifth aspect of the present invention may further comprisewater. Water may be present in an amount sufficient to dissolve theorganic material. Desirably, water is present in the minimum amountrequired to dissolve the organic material in order to minimize theamount of water introduced into the composition.

The organic material may include a carbonate ion or a carbonate species.

The organic material may have high alkalinity and also chelate or bondwith a metal substrate and/or with an active ingredient in the electrodelayer.

The organic material may comprise a guanidine compound. Guanidine(NHC(NH₂)₂) includes an imide group and aminal or aminoacetal groups.The organic material may comprise guanidine carbonate. Guanidinecarbonate has the formula (NHC(NH₂)₂)CO₃(NHC(NH₂)₂). It is highlyalkaline, exhibiting a pH of 11 to 12 when prepared as a 5% solution inwater. It has a solubility in water of approximately 40 to 45 g per 100g of water.

The organic material may have high alkalinity when dissolved in water.In some embodiments, the organic compound exhibits a pH of at least 8when dissolved as a 1 M solution in water, more preferably a pH of atleast 9, more preferably a pH of at least 9.3, even more preferably a pHof at least 10, or at least 11 or at least 12, when dissolved as a 1 Msolution in water. In other embodiments, the organic compound exhibits apH of at least 8 when dissolved in water, such as when dissolved inwater as a 5% by weight solution in water, more preferably a pH of atleast 9, more preferably a pH of at least 9.3, even more preferably a pHof at least 10, or at least 11 or at least 12, when dissolved in water,such as when dissolved in water as a 5% by weight solution in water.

Other organic materials, with high alkalinity and chelating propertiesmay include ethylenediamine, trymine, trymidine, histidine, aminoaceticacid, ammonia, N-butylamine, methylamine, piperidine, triethylamine,diethanolamine, EDTA, etc. It may also be possible to combine twocompounds where one supplies the high alkalinity and the other providesthe strong chelating properties.

In a sixth aspect, the present invention provides a method for formingan electrode for use in a lithium ion battery, the method comprising thesteps of providing a metal substrate and applying a coating of electrodematerial to the metal substrate, wherein the coating of electrodematerial applied to the metal substrate comprises a composition asdescribed with reference to the first aspect of the present invention,the second aspect of the present invention, the third aspect of thepresent invention, the fourth aspect of the present invention or thefifth aspect of the present invention.

The organic material may be at least partly dissolved in water at thetime of applying the coating to the metal substrate.

The metal substrate may comprise an aluminium substrate or a coppersubstrate.

The metal substrate may comprise aluminium or an aluminium alloy. Themetal substrate may comprise aluminium foil or a foil made from analuminium alloy. The metal substrate may also comprise copper or acopper alloy. The metal substrate may comprise copper foil or a foilmade from a copper alloy.

The electrode coating may be applied to the metal substrate by sprayingor by printing.

The method may further comprise the step of subjecting the coated metalsubstrate to a calendering step to increase the density of the electrodematerial coating. The calendering step may comprise pressing or rolling,optionally with heating.

In a seventh aspect, the present invention provides a lithium batterycomprising a first electrode, a second electrode and an electrolytecontaining a lithium compound, wherein at least one of the electrodescomprises a metal substrate having an electrode material coated thereon,the electrode material comprising a coating formed from a composition asdefined in any of the first aspect of the present invention, the secondaspect of the present invention, the third aspect of the presentinvention, the fourth aspect of the present invention or the fifthaspect of the present invention.

The present inventors have found that there is typically a minimumamount of organic material that must be added to the composition inorder to obtain good adhesion on the substrate. It is expected that aminimum amount of about 1% by weight of the organic material will berequired to obtain good adhesion, typically at least 1.5% by weight oreven at least 1.8% by weight, or even at least 2% by weight. If theorganic material is present in the composition as a solution, it ispossible to use a smaller amount to obtain good adhesion than if theorganic material is present in the composition as a solid. However, goodadhesion can still be obtained when the organic material is present inthe composition as a solid. The percentage of organic material added isexpressed as a weight percentage of the weight of the electrodematerial/composition.

The composition of the present invention may be used on a cathode or onan anode. The battery electrode in accordance with embodiments of thepresent invention may be a cathode or an anode.

In another aspect, the present invention provides a battery electrodefor a lithium ion battery comprising an electrically conductivesubstrate having an electrode layer applied thereto, characterized inthat the electrode layer includes an organic material having highalkalinity, or an organic material which can be dissolved in organicsolvents, or an organic material having an imide group(s) andaminoacetal group(s), or an organic material that strongly chelates orbonds with a metal substrate and/or chelates or bonds with an activematerial in the electrode layer, such as the conductive particulatematerial (which may be a carbonaceous material).

In all aspects of the present invention, the organic material maycomprise an organic compound (such as a single organic compound) or twoor more organic compounds.

It has also been found that it might not be necessary to mix the organicmaterial in with the other materials for the electrode layer prior toapplying the electrode materials to the electrode layer. In particular,satisfactory adhesion has also been achieved by applying the organicmaterial to a substrate (for example, by spraying or brushing or wiping)and subsequently applying the electrode layer to the substrate. Inanother aspect, the present invention provides a method for forming anelectrode for a lithium ion battery comprising the steps of applying toa substrate an organic material having high alkalinity, or an organicmaterial which can be dissolved in organic solvents, or an organicmaterial having an imide group(s) and aminoacetal group(s), or anorganic material that strongly chelates with a metal substrate, andsubsequently applying an electrode material to the substrate. In thisaspect, the composition that is applied to the substrate may be thoughtof as including the organic material and the other electrode materials,but with the composition applied in two different steps.

In all aspects of the present invention, it may be preferable that theorganic material does not have counter-ions, such as Na or K, whichinduce unwanted reaction with aluminium or the electrolyte.

Throughout this specification, the term “composition” is used to referto an intimate mixture of the components of the composition as well asto the components of the composition being present in two or moreregions, layers or volumes, with intermixing at the edges, or to acomposition showing a stratified composition.

Throughout this specification, the composition may be applied to asubstrate by applying an intimate mixture of all the components of thecomposition to the substrate or by applying one or more components tothe substrate followed by sequential application of one or morecomponents, or by applying the organic material (in solid form, inorganic

solution form or in aqueous solution form) to the substrate, followed byapplication of one or more other components in a single further step orin two or more further application steps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a graph of electrical resistance of pressed pellets ofplain LFP powder vs pressure, which demonstrates a gradual reduction ofresistance with increased pressure;

FIG. 2 shows a photograph of a GC solution placed in contact with NMP.The GC displays an immediate very fine precipitation;

FIG. 3 shows a photograph of the apparatus used to coat the electrodematerial composition onto the aluminium substrate, as described inExample 3;

FIG. 4 schematically shows the steps involved in assembling a test cellused in Example 4;

FIG. 5 shows a graph of voltage vs capacity for an electrode materialcontaining 1.6% GC, as described in Example 5;

FIG. 6 shows photographs of test electrodes made using an electrodecomposition having 1% GC added as a solid (top photograph), 1% GC addedas a 1 M solution (middle photograph) and 1.34% GC added as a 1 Msolution (bottom photograph); and

FIG. 7 shows the difference between the carbon pre-coating (bottomphotograph) and stripped coating (top photograph), as used inComparative Example 8.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention will now be described.

In the following description, reference to “good adhesion” is to betaken to mean that the coating shows no sign of detachment of thebattery cathode coating from the aluminium substrate after the hardpress rolling or calendering.

In experimental work conducted by the present inventors, guanidinecarbonate was used as the organic material that was added to theelectrode material composition. Adding guanidine carbonate was found tosignificantly enhance the adhesion of the electrode material to thealuminium substrate without adversely affecting the electricalproperties of the electrode material. Furthermore, the coating wasachieved by simply adding guanidine carbonate, typically in the form ofan aqueous solution of guanidine carbonate, to the electrode materialcomposition that was being applied to the aluminium substrate.Therefore, no additional processing steps (beyond adding the solution ofguanidine carbonate) are required to form the electrodes.

Guanidine carbonate is a very unique organic carbonate. It is one of thestrongest alkaline compounds, which translates into smaller amountsrequired to obtain a given high pH.

Surprisingly, the present inventors have found that addition of a smallamount of guanidine carbonate dissolved in water (for example, 1.6 wt %of the standard paste) to the standard cathode paste formulationenhanced the adhesion and produced smooth surfaces after hard pressing.Surprisingly, addition of dry guanidine carbonate did not work at lowerlevels of guanidine carbonate addition.

Without wishing to be limited by theory, the present inventors believethat guanidine carbonate is playing multiple roles. The high alkalinityof guanidine carbonate would result in some degree of locally exothermicinterface reaction and dissolution of the aluminium oxide surface layerpresent on the aluminium substrate, likely creating surface roughness onthe aluminium substrate. In addition, by cleaning the oxide layer (whichis electrically insulating by nature) in-situ and during the process ofcoating the electrode material onto the substrate, the electricalconnection between the cathode material and the aluminium currentcollector would be enhanced.

Other highly alkaline organic compounds would be expected to worksimilarly to guanidine carbonate with respect to generating surfaceroughness, although higher concentrations are likely to be required ifthose other highly alkaline organic compounds have a lower alkalinitythan guanidine carbonate. Some very acidic solutions would be expectedto work too, although one of the abovementioned prior art documentsteaches against the use of acids because H⁺ ions compete for space withLi⁺ ions.

In general, care must be taken that whatever the compound or compoundschosen to do a job equivalent to guanidine carbonate, it does not haveother unwanted side reaction with the substrate or the electrolyte. Theelectrolyte is typically LiPF6 salt dissolved in a mixture of Diethylcarbonate (DEC), Ethylene carbonate (EC) and/or propylene carbonate(PC). Without limitation by theory, the fact that these carbonates arealready present in the electrolyte appears to indicate a possiblecompatibility of guanidine carbonate with the electrolyte.

Another characteristic of guanidine carbonate that may be contributingto a strong adhesion is that guanidine carbonate has strong chelatingproperties with metals, which may allow it to bond strongly withaluminium and iron in the substrate and the LFP particles, respectively.

Due to the chelating property of guanidine carbonate and the presence ofcarbonate, some affinity to the carbon particles leading to theirfunctionalization and allowing a more homogeneous mixing is alsofeasible. Monarch 1300, which is a functionalized particulate carbonthat has been surface treated with acid, leads to good adhesion.Unfortunately it is not as good an electrical conductor as Super P Li(which is another carbon black material that is commonly used in themanufacture of electrodes for lithium ion batteries). Super P Li carbonblack is specially optimized for Lithium ion battery applications andhence battery manufacturers frequently use this carbon black material.

In another embodiment of the invention, addition of a small amount ofLiOH dissolved in water to the standard cathode paste was found toenhance adhesion, although migration of Li during electrochemicaltesting may undo the benefit of the good adhesion. For very similarreasons, it is, in general, preferable to avoid the presence ofcounter-ions such as Na and K, which may induce other unwanted reactionwith aluminium or the electrolyte. Accordingly, in another aspect, theorganic material suitably does not have counter-ions which induceunwanted reaction with aluminium or the electrolyte.

In summary, and again without wishing to be bound by theory, guanidine.carbonate appears to play simultaneous roles, each of which enhances theadhesion of the cathode material paste to the aluminium substrate (orthe anode material paste to the copper substrate, respectively).Adhesion enhancement mechanisms obtained with very small amounts ofguanidine carbonate could possibly include cleaning of the oxide surfacelayer of aluminium (or copper), roughening of the interface, chemicalbonding to the cathode (or anode) material particles and to thesubstrate and probably functionalization of the carbon additiveparticles as well.

Spherical particles would in general be expected to requiresignificantly more binder than flat particles, since the contact wouldbe more point like for the spherical particle. However, if a simplemethod, such as the one provided in this invention, is established forgood adhesion of spherical particles, without requiring any extrabinder, it could potentially become the method of choice to optimize ina controlled fashion the packing density and porosity of coated cathodematerials by appropriate selection of particle size distributions.

EXAMPLES

In the following examples, a battery cathode is manufactured by applyinga coating of the electrode material to an aluminium substrate.

Example 1 Preparation of Cathode Paste Formulation—using GuanidineCarbonate

For a 10 g target (LFP+PVDF+Super P Li) of a 90:5:5 (LFP:PVDF:Super PLi) electrode mix, the following table gives the relative quantities ofthe ingredients:

PVDF 0.50 g NMP 24 g 1M Guanidine carbonate solution 23 drops* Super PLi 0.50 g LFP powder 9.00 g *4 drops weigh 0.1 g

Procedure:

Make up a stock IM Guanidine carbonate (GC) solution by dissolving 18 gGC and adding reverse osmosis (RO) water up to a volume of 100 ml in avolumetric flask. A GC solution close to IM can be obtained bydissolving 18 g of GC in 88.66 g of RO water. The resulting pH is around11.5.

Weigh out the PVDF and then add the proper amount of NMP.

Using the High Speed Mixer (HSM) whiz this mixture until PVDF hasdissolved into NMP.

Add the IM Guanidine carbonate solution drops and blend with UltraTurrax (UT), setting 1, or equivalent dispersion equipment, untildispersed

Weigh out Super P Li carbon black and add this to the PVDF/NMP/GCsolution. Continue HSM until mixture is a smooth paste (approx 5 min).

Weigh out the active material (e.g. LiFePCU or other lithium containingmaterial) and using a mortar and pestle, gently grind the material for afew minutes to ensure there are no large agglomerates in powder.

Add this powder to the Super P/PVDF/NMP/GC mix. Gently mix using aplanar mixer for at least 1 hour, ensuring that all the material is wellmixed.

Example 2 Preparation of Cathode Paste Formulation—Adding GuanidineCarbonate After Completing the Regular Paste Mix

A similar paste formulation procedure to that described in example 1 isfollowed with the only difference that GC solution is added later. Aftera uniform paste without GC has been prepared, the correct amount of GCsolution is added and mixed thoroughly. The amount of GC is aimed at thesame proportions of example 1 and it can be determined according to thefollowing proportions:

Weigh 6 g of Super P/PVDF/NMP/Active Material mixture into small beaker(50 ml beaker).

Add 0.1 g of 1 M GC (4 drops) and mix well.

Follow Electrode coating procedure (using bare Al foil) to completecathode using this mixture.

In this case the coating displays good adhesion, but the coating usuallyhas slightly less smooth surface than the coating arising from thecomposition of example 1, depending on the degree of mixing andhomogeneity of the guanidine carbonate (GC) additive. Drops of GCsolution when in contact with NMP display immediate very fineprecipitation (see FIG. 2). This fine precipitate would appear easier todistribute homogeneously in the process described in example 1.

Example 3 Electrode Coating

The following procedure was followed to coat an electrode with theelectrode coating composition. FIG. 3 shows a photograph of theapparatus used to coat the electrode material composition onto thealuminium substrate:

Cut a strip of aluminium foil to the appropriate size.

Squirt a small amount of water/acetone onto a glass plate and lay thealuminium strip on top of it. Adhere the strip to the glass plate bysqueezing out the excess water/acetone from underneath with a foldedpaper towel. Smooth the edges of the Al strips with the cap of a pen.

Set the micrometers on the graded doctor blade to 25 microns. Place asufficient amount of electrode paste onto the Al foil; place the doctorblade in front of it, and with a steady continuous movement spread thecoating all the way along the strip.

Carefully transfer the strip onto a glass tray and place weights oneither end to ensure foil does not curl whilst drying.

Place in oven at 150° C. in air for at least 1 hour.

Using a calendaring (roller press) machine press electrodes. Once theelectrodes have been pressed, use the steel disc from the battery cellas a template to cut out electrode disks. The weight and height of eachdisc needs to be measured and recorded.

Place the discs in the ante-chamber under vacuum at 150° C. for 48 hoursprior to battery test-cell assembly inside dry atmosphere glove box.

The unassembled battery test-cell units should also be pre heated for atleast 24 hours, prior to assembly. This can be done at the same time asthe electrodes if possible.

Example 4 Battery Test Cell Assembly Procedure

Transfer unassembled battery test cell and electrodes from theante-chamber into glove box.

Cut out separators using hole punch. Place in ante-chamber under vacuumat 80° C. for a minimum of 24 hrs.

In glove box, prepare anodes (lithium ribbon). Using fine sand paper,clean a strip of lithium ribbon and use a hole punch to cut out anodes.

Fill beakers with a small amount of electrolyte (LiPF₆ in EC/DEC). Soakthe first electrode in one of the beakers for about 5 mins beforefollowing the assembly procedure below.

Assemble cells (follow numbering from 1-6 first, as shown in FIG. 4) asbelow without screw cap.

Place soaked electrode in bottom of cell.

Soak the separator in electrolyte before placing it on top of thecathode.

Push Teflon holder into place over the spacer and cathode.

Place anode in Teflon holder, making sure that it is flush on thespacer.

Insert steel disk on top of anode and push down gently.

Using micropipette, put 2 C % il of electrolyte around the outside ofthe Teflon holder. Use the fresh electrolyte in the second beaker.

Place top plate on cell and tighten wing nuts.

Leave screw caps off for time being and assemble remaining cells.

Once all cells have been assembled, wait 1 hr.

Connect positive and negative leads to battery cells and tighten screwcaps.

Calculate current for desired charge rate and enter into program. Startcycling for that channel and then repeat for remaining channels.

When cycling is finished, save the data and calculate the capacity(mAh/g) for charge and discharge and for all cycles.

Once cycling is complete, take cells out of Glove Box. Clean and preparecells for next experiment.

Note: Use 2 sets of vinyl gloves when dealing with electrolyte.

Example 5 Battery Cathode Properties

The test cell is typically tested under what is known as a half-cellconfiguration with Li metal as anode. Voltages are swept between 2.5Vand 4.2V. Currents are constant during a charge and a discharge cycleand are estimated, based on the loading of active material, to giveC/10, C/5/C/2,C, 2 C, 4 C, 8 C, 10 C, 12 C, 16 C, etc. In most cases,the charge and discharge for a full cycle are kept at the same current,although it is also possible to charge at a fixed current (often C/2 orC/5) and discharge at the various multiples of C (C=capacity). Theresults are shown in FIG. 5 for an electrode composition that includes1.6% GC.

Comparative Example 1 Preparation of Standard Cathode PasteFormulation—without Guanidine Carbonate

A similar paste formulation procedure to that described in Example 1 isfollowed, with the only difference that the guanidine carbonate additiveis not included. Then the electrode coating procedure as described inExample 3 is followed. In this case, the coating displays pooreradhesion.

As a reminder, reference to adhesion is often made with respect to theresults obtained after hard pressing or calendering. As mentioned above,a simply dried coating may appear to adhere and to have a smoothsurface. Although, gentle or no calendering gives apparently uniform,smooth coatings, these coatings often get detached in later test cellassembly and in general, the tape density will be very low, which isundesirable for applications.

Comparative Example 2 Preparation of Cathode Paste Formulation—WithWater Drops Addition

A similar paste formulation procedure to that described in Example 1 isfollowed with the only difference that pure water drops are used insteadof Guanidine carbonate solution. Then the electrode coating procedure asdescribed in Example 3 is followed. In this case the coating did notadhere.

Comparative Example 3 Preparation of Cathode Paste Formulation—with DryGuanidine Carbonate

A similar paste formulation procedure to that described in Example 1 isfollowed with the only difference that solid Guanidine carbonate withoutwater is added instead of GC solution. Then the electrode coatingprocedure as described in Example 3 is followed. In this case thecoating did not adhere for 1.3 w % added as solid (see FIG. 6). However,by significantly increasing the weight percentage of dry GC, it ispossible to obtain improved adhesion. FIG. 6 shows photographs of testelectrodes made using 1% GC added as a solid (top photograph), 1% GC.added as a 1 M solution (middle photograph) and 1.34% GC added as a 1 Msolution (bottom photograph). Best adhesion was found with 1.34% GCadded as a solution, followed by 1% GC added as a solution, followed by1% GC added as a solid.

Comparative Example 4 Preparation of Cathode Paste Formulation—WithLower Amount of Guanidine Carbonate

A similar paste formulation procedure to that described in Example 1 isfollowed, with the only difference that a lower amount of guanidinecarbonate solution is used. Then the electrode coating procedure asdescribed in Example 3 is followed. In this case, lower amounts of GC(below about 1 wt %) displayed degraded adhesion, roughly in proportionto the reduced amount of GC (see FIG. 6).

Comparative Example 5 Preparation of Cathode Paste Formulation—with LiOHAddition

A similar paste formulation procedure to that described in Example 1 isfollowed, with the only difference that LiOH solution instead ofguanidine carbonate solution is used. The amount of LiOH was estimatedto produce a similar pH as that obtained with GC.

Then the electrode coating procedure as described in Example 3 isfollowed. In this case, the sample displayed good adhesion.

Comparative Example 6 Preparation of Cathode Paste Formulation—with KOHAddition

A similar paste formulation procedure to that described in ComparativeExample 5 is followed, with the only difference that KOH solutioninstead of LiOH solution is used. Then the electrode coating procedureas described in Example 3 is followed. In this case, the sample did notdisplay as good adhesion.

Comparative Example 7 Preparation of Cathode Paste Formulation—withoutGuanidine Carbonate but with Monarch 1300 Instead of Super P Li

A similar paste formulation procedure to that described in ComparativeExample 1 is followed, with the only difference that Monarch 1300 isused as the conductive carbon additive instead of Super P Li. Then theElectrode coating procedure as described in Example 3 is followed. Inthis case, good adhesion is obtained with Monarch 1300, however,electrical and electrochemical properties are inferior.

Comparative Example 8 Preparation of Carbon Pre-Coat on AluminiumSubstrate

Make up the following solutions:

Solution A LUDOX ® AM-30 suspension 10 g Sigma 420875-4L (colloidalsilica) Solution B Potassium hydroxide 0.56 g Water 10 g Solution CWater 5 g 85% H₃PO₄ 1 g

Add Solution A to Solution B.

Stir for 1 minute, then slowly add drop-wise, 85% H₃PO₄, waiting 2minutes between each drop for 11 drops. Check the pH.

Note: This should drop the pH to approximately 10.4-10.6.

From here use Solution C to slowly reach pH 9.6-10 (don't worry abouttiming in this part). The solution will gel after a few minutes. Ensurethat the final pH is recorded. Note: Try and have the pH stable around10, before the solution gels, otherwise the pH measurement may not beaccurate.

Then add 12 g of water and mix thoroughly before adding 1 g SuperP Li.

Break up the gel and blend for about 5 min with high-speed mixer(setting 3) to thoroughly disperse.

To produce a thin coating, set the doctor blade to 5-10 microns on themicrometers. Squirt a small amount of water onto a glass plate and layan aluminium strip on top of it. Adhere the strip to the glass plate bysqueezing out the excess water from underneath with a folded papertowel. Smooth the edges of the Al strips with the cap of a pen. Thenspread sufficient pre-coat material on one end of the strip; place thedoctor-blade in front of it, and with a steady continuous movementspread the coating all the way along the strip.

Allow the wet Pre-coat to air dry, then place in a 150° C. oven and dryfor at least 1 hour.

Hold down both ends of the strip in place with sticky tape,

Then apply lengths of sticky tape to the coated surface, press downfirmly.

Peel off tape to remove the loose and excess carbon. Do this twice. Thestrips are now ready to coat with the Battery Material.

FIG. 7 shows the difference between the original carbon pre-coating(bottom photograph) and stripped coating (top photograph).

Comparative Example 9 Electrode Coating on Carbon Pre-Coated AluminiumSubstrate

A similar electrode coating procedure to that described in Example 3 isfollowed with the only difference that carbon pre-coated aluminium isused instead of bare aluminium.

When using super P Li in the pre-coat and in the cathode pasteformulation, properties nearly as good as those with the method of theinvention here were obtained. However, since the carbon pre-coat issomewhat sensitive to the peel off of loose particles, thereproducibility of the GC method was superior. The carbon pre-coatedsubstrate often had small, local inhomogeneities, probably as a resultof the difficulty in mixing once the intermediate carbon pre-coat pastegels up.

Comparative Example 10 Electrode Coating on Carbon Pre-Coated AluminiumSubstrate

In order to test the effect on performance further various combinationsof Monarch 1300 and Super P Li in the carbon prc-coat and in the pasteformulation were produced as described in Comparative example 9 with thecorresponding type of carbon. Results are summarized in the followingtable:

TABLE Pre- Paste Sample coat carbon mix carbon Electrical propertiesExample 9 Super P Li Super P Li Low impedance, good discharge platformExample 10a Super P Li Monarch 1300 Higher impedance, poorer dischargeplatform Example 10b Monarch Super P Li Higher impedance, poorer 1300discharge platform Example 10c Monarch Monarch 1300 Much higherimpedance, 1300 significantly poorer discharge platform

Comparative Example 11 Anode Manufacture without Guanidine Carbonate

In this example, Super P Li (0.2 g) was mixed into NMP (15.82 g) using ahigh speed mixer for 1 min. Cpreme graphite G5 (9.2 g) was then mixedinto this solution also using a high speed mixer for 1 min. This mixturewas then added to a slurry of NMP (5.25 g)+PVDF (0.6 g) that had beenhigh speed mixed for 1 min. This final slurry was mixed using a Planarmixer for 20 mins. Electrodes were then coated using a doctor blademethod onto Copper foil substrate at varying settings and dried on a hotplate at 105° C.

After pressing the electrodes using a roll press, all electrodesdelaminated and failed.

Example 12 Anode Manufacture with 1.74% wt Guanidine Carbonate

In this example, PVDF (0.6 g) was dissolved into NMP (21 g) using highspeed mixing. Super P Li (0.2 g) was then added to this solution andhigh speed mixed for 1 min. Cpreme G5 Graphite (9.2 g) was then addedusing a Planar mixer for 1 hr. 1 M Guanidine Carbonate (0.51 g) was thenadded to final solution and planar mixed for another 1 hr. Electrodeswere then coated using a doctor blade method onto a copper foilsubstrate at varying settings and dried on a hot plate at 110° C.

After pressing the electrodes using a roll press, the adhesion of thematerial onto the copper foil showed significant improvement fromComparative Example 11.

Example 13 Cathode Manufacture with 1.74% wt Guanidine Carbonate usingReduced Mixing Times

In this example, PVDF (0.5 g) was dissolved into NMP (21 g) using highspeed mixing. Super P (0.5 g) was then added to this solution and highspeed mixed for 1 min. Active material (9.0 g) was then added using aPlanar mixer for 5 mins. 1.74 wt % of 1 M Guanidine Carbonate (0.54 g)was then added to final solution and planar mixed for another 5 mins.Electrodes were then coated using a doctor blade method onto aluminiumfoil substrate at varying settings and dried in oven at 120 C using aslow temperature increase (Approx 1 hr→120° C., 30 mins at 120° C.).

Excellent adhesion on the electrode was seen after roll pressing.

Example 14 Cathode Manufacture with 1.74% wt Guanidine Carbonate UsingReduced Mixing Times

In this example, PVDF (0.5 g) was dissolved into NMP (21 g) using highspeed mixing. Super P Li (0.5 g) was then added to this solution andhigh speed mixed for 1 min. Active material (9.0 g) was then added usinga Planar mixer for 2 hrs. 1.74 wt % of 1 M Guanidine Carbonate (0.54 g)was then added to final solution and planar mixed for another 5 mins.Electrodes were then coated using a doctor blade method onto Aluminiumfoil substrate at varying settings and dried in oven at 120 C. using aslow temperature increase (Approx 1 hr→120° C., 30 mins at 120° C.).

Excellent adhesion on the electrode was seen after roll pressing.

Example 15

Excellent adhesion of active material pastes can also be achieved by airbrush coating of GC solutions onto aluminium substrates according to thefollowing procedure:

A specific concentration of GC solution (e.g. 1 M) is loaded into agravity fed air bush.

Atomization is optimized so as to minimize beading of the solution whensprayed onto aluminium foil.

A single layer of the GC solution is spray coated onto an aluminium foilsubstrate. The active material paste is then immediately doctor bladecoated over the wet GC film.

Film is dried according to normal procedure.

Those skilled in the art will appreciate that the present invention maybe susceptible to variations and modifications other than thosespecifically described. It will be understood that the inventionencompasses all such variations or modifications that fall within itsspirit and scope. The invention also extends to all combinations offeatures described herein.

What is claimed is:
 1. A battery electrode composition for forming abattery electrode for a lithium ion battery the composition comprising:a lithium containing compound that provides a lithium ion source in thebattery; a binder; a solvent; a conductive particulate material; and anorganic material having high alkalinity or LiOH; wherein the compositionupon being applied to a substrate binds to the substrate thereby formingthe electrode.
 2. A method for forming a battery electrode comprising asubstrate and a battery electrode composition comprising a lithiumcontaining compound that provides a lithium ion source in the battery; abinder; a solvent; a conductive particulate material; and an organicmaterial having high alkalinity or LiOH, the battery electrodecomposition being applied to the substrate to form the electrode layeron the substrate.
 3. A method for forming a battery electrode comprisingproviding a battery electrode composition comprising a lithiumcontaining compound that provides a lithium ion source in the battery; abinder; a solvent; a conductive particulate material; and an organicmaterial having high alkalinity and applying the organic material to asubstrate thereby forming the electrode layer on the substrate.
 4. Abattery electrode for a lithium ion battery comprising an electricallyconductive substrate having an electrode layer applied thereto, whereinthe electrode layer includes an organic material having high alkalinity,or an organic material having an imide group(s) and aminoacetalgroup(s), or an organic material that strongly chelates or bonds with ametal substrate and/or chelates or bonds with an active material in theelectrode layer.
 5. A battery electrode as claimed in claim 4, whereinthe organic material chelates with or bonds with a conductive additivein the electrode layer.
 6. A battery electrode as claimed in claim 1,wherein the organic material chelates with or bonds with a binder in theelectrode layer.
 7. A battery electrode as claimed in claim 4, whereinthe organic material is selected from the group consisting of guanidinecarbonate, ethylenediamine, trymine, trymidine, histidine, aminoaceticacid, ammonia, N-butylamine, methylamine, piperidine, triethylamine,diethanolamine, EDTA, and mixtures of two or more thereof.
 8. A batteryelectrode as claimed in claim 1, wherein the organic material isselected from the group consisting of guanidine carbonate,ethylenediamine, trymine, trymidine, histidine, aminoacetic acid,ammonia, N-butylamine, methylamine, piperidine, triethylamine,diethanolamine, EDTA, and mixtures of two or more thereof.
 9. A batteryelectrode as claimed in claim 1, wherein the organic material has one ormore imide groups and one or more aminoacetal groups.
 10. A batteryelectrode as claimed in claim 4, wherein the organic material has one ormore imide groups and one or more aminoacetal groups.
 11. A batteryelectrode in accordance with claim 1 wherein the organic materialcomprises a guanidinium compound.
 12. A battery electrode in accordancewith claim 4 wherein the organic material comprises a guanidiniumcompound.
 13. A battery electrode in accordance with claim 11 whereinthe guanidinium compound comprises guanidine carbonate.
 14. A batteryelectrode in accordance with claim 12 wherein the guanidinium compoundcomprises guanidine carbonate.
 15. A battery electrode as claimed inclaim 14, wherein the guanidine carbonate is present in an amount offrom 0.3% to 2.0% by weight of the electrode layer.
 16. A batteryelectrode as claimed in claim 4, wherein the battery electrode comprisesan anode.
 17. A battery electrode as claimed in claim 4, wherein thebattery electrode comprises a cathode.
 18. A battery electrode asclaimed in claim 4, wherein the electrode layer comprises a materialthat intercalates lithium.
 19. A battery electrode as claimed in claim4, wherein the electrode layer further comprises a binder and a solvent.20. A battery electrode as claimed in claim 4, wherein the electrodelayer further comprises a conductive particulate material.
 21. A batteryelectrode as claimed in claim 4 wherein the organic material isincorporated into the electrode material as a solution of the organicmaterial dissolved in water.
 22. A method for forming a batteryelectrode as claimed in claim 4 wherein the electrode layer includes anorganic material having high alkalinity, or an organic material havingan imide group(s) and aminoacetal group(s), or an organic material thatstrongly chelates or bonds with a metal substrate and/or chelates orbonds with an active material in the electrode layer, the methodcomprising producing a composition including the organic materialwherein the composition is applied to the substrate to form theelectrode layer on the substrate.
 23. A battery electrode for a lithiumion battery comprising an electrically conductive substrate having anelectrode layer applied thereto, wherein the electrode layer includes anorganic material having high alkalinity, or an organic material havingan imide group(s) and aminoacetal group(s), or an organic material thatstrongly chelates or bonds with a metal substrate and/or chelates orbonds with an active material in the electrode layer, wherein theorganic material comprises a guanidinium compound.
 24. A method forforming a battery electrode for a lithium ion battery, the methodcomprising: applying an electrode layer to an electrically conductivesubstrate wherein the organic material comprises a guanidinium compound.